Milo g



(N0 Modl.)

M. G. KELLOGG.

MULTIPLE SWITOHBOARD. I No. 592,308. Patented Oct. 26,1897.

[z/wM. 25 LggzA/ M L MJz H (d7. V l

NlTED STATES FFICE,

PATENT MILO G. KELLOGG, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE KELLOGGSWITCIIBQARD AND SUPPLY COMPANY, OF SAME PLACE.

M ULTIPLE SWITCHBOARD.

SPECIFICATION formingpart of Letters Patent No. 592,308, dated October26, 1897. Application filed July 16, 1888. Renewed December 2 0, 1890.Serial No. 375,311. (No model.)

To aZZ whom, it may concern.-

Be it known that I, MILO G. KELLOGG, of Chicago, (Hyde Park,) Illinois,have invented certain newand useful Improvements in MultipleSwitchboards for Telephone-Exchanges, of which the following is a full,clear, concise, and exact description, reference being had to theaccompanying drawings, forming a part of this specification.

My invention relates to a telephone exchange system in which thesubscribers lines are metallic-circuit lines connected to multipleswitchboards and it consists in a system of testing at any board todetermine whether any line is in use.

I place as many switchboards in the central office as are foundnecessary or desirable in order to. properly answer the calls andconnect and disconnect the subscribers lines. On each board I place foreach line a springjack or similar switch having two insulatedcontact-points which are normallyin contact and a third contact point orpiece normally insulated from the others except by the line connections,said switch being adapted to receive a lo0p-switch plug and, when theplug is inserted, to disconnect the switch-points which are normally incontact and connect one of them to one of the contact-pieces of the plugand at the same time connect the other contact-piece of the plug withthe third contact point or piece of the switch mentioned above.

The third contact points or pieces of the switches above described areso placed and arranged that an operator may at will apply a test-plug orsimilar device to them.

The switches of a line on the different boards may be calleda series ofswitches, and the test-pieces of a line may be called a series oftest-pieces.

At each subscribers station is a battery which for purposes of testingshould be in the circuit of his line when it is not in use and which maybe in said circuit all of the time.

Figures 1 and l of the drawings are front views of sections of twomultiple switchboards to which the same wires are connected. Fig. 2 is adiagram of the boards and the cir cuits and connections necessary toillustrate my invention. Fig. 3 shows a double or loop plug adapted tobe used with the switches. Fig. 4: is a diagram of a subscribefs-stationapparatus necessary to illustrate my invention.

In the drawings like parts and apparatus are indicated by the sameletters and figures of reference.

In Fig. 2, A is a sectional view of the switchboard shown in Fig. 1, andA is a sectional View of the switchboard shown in Fig. 1", each asindicated by the line cl e.

a I) represent rubber strips, of the shape substantially as shown, onwhich the metal parts of the spring-jack switches are mounted. Thesestrips may be of a length to receive any convenient number ofspring-jack parts.

Z l, &c. are square holes through the fronts of and at the edges of thestrips adapted to receive and guide the switch-plugs. Thecontact-springs g g, &c., are mounted to the rear of and are parallel tothe holes Z Z, &c., to which they belong, as shown. The contactpoints ith, 860., corresponding to the contactsprings pass through the rubberstrips, as shown, and are connected with the connecting-pieces 7t h.

jj are the contact-pieces of the switches,insulated from the rest of theparts except by the line-wire, each adapted to connect one side of itsline to one of the contact-pieces of a loop-plug when inserted, and alsoto be the test-piece of its line at its board. The switchplugs aresubstantially as shown in Fig. 3.

The several parts mentioned above are so made, shaped, arranged, andadjusted that when a plug is inserted into any switch-hole it raises thespring in the rear of the hole from the contact-point, (on which itnormally rests,) and the spring is connected to one of thecontact-pieces of the plug, while the other contact-pieceof the plug isconnected to the contact-piece j of the switch which is used. Eachsection of a rubber strip, with its contact-spring, contact-point,contact-piece, and

the hole, all arranged and operating as shown,

one plug at each board, and each plug connected to one side of its testreceiving instrument by a flexible cord, as shown. The plugs and cordsare so Constructed that the operators may at will bring the metal'tipsof the plugs in contact with any contact-pieces at their respectiveboards.

In the subscribers-station apparatus shown in Fig. 4, 1 is thetelephone-switch, 2 is the subscribers hand-telephone, 3 is thebatterytransmitter, 4 is the primary of its inductioncoil, 5 is thesecondary of its'induction-coil, and 6 is the transmitter-battery. Thecontact-points of the switch and the circuits aresubstantially as shown.The calling generator and bell are not shown, as they are not necessaryto illustrate the operation of the test system. Line No. 1 andfline No.l represent the two sides or branches of the mej tallic-c-ircuit line ofthe subscriber. It will be seen that the battery is in the circuit ofthe line, as is also the battery-transmitter and primary of theinduction-coil, and that when the telephone is off from its switch ashort local circuit is closed, in which is the battery,

the transmitter, and primary of the inductioncoi-l, and that the batterytherefore operates as a transmitter-battery. It also operates as atest-battery for its line, as will hereinafter appear.

The circuit of each subscribers line may be traced as follows: Onebranch, starting out from one side of the subscribers-station apparatus,is connected with all the contactpiecesjj or the switches of the line onthe several boards. out from the other side of the subscribers-stationapparatus, passes successively through the pairs of contact-pointsnormally in con tact of its switches on'the several boards, be ingconnected in each case to thespring g first. From the last contact-pointh the line passes or is connected to all the test receiving instrumentson the several boards on the other side of the instruments from whattheir test-plugs are connected. The connections, lineNo. 1* and line No.1 in Fig. 2, are for the line ofwhich thesubscribers-station apparatusshown in Fig. 4 is a part.

The lines and the test receiving instruments are not normally;grounded,but the test receivinginstruments are open to the v groundatthe central'oftice, andian accidental ground on the line tested betweenthe sub-- scribers-station and the pairs of line-switchcontact-pointswould not occasion, on testing, a false-signal that theline was free when it was switched at the centraloffice, as would be thecase were the test receiving instruments'connectedwiththe: ground at thecentral office It is well known that such accidental grounds. are liableto occur on metal liccircuits, but in the system described above such agroundwouldnot affect the testing or otheroper-ation of; the system.

Itisapparent that eachline is normally The other branch, starting openat the central ofiice and that its battery is on closed circuit onlywhen in use. It is also apparent that when a test-plug is applied to thecontact-piece j of any line and the line is not switched there is acomplete circuit through the line, the subscribers bat- 3 tery, back tothe central office, and through the pairs. of contact-points of theswitches of the line and the test receiving instrument to which the plugbelongs, and the instrument being energized by thebattery will respondand indicate that the line is not in use. If, on the other hand, theline is switched at any 3 board, this test-circuit is opened at the pairof contacts at the board where the line is switched and the instrumentwill not respond. The operator will then know that the line is in useand will'not connect to it.

I have not indicated in detail the calling .apparatus or the operatorsanswering and j connecting apparatus, as it is not necessary f to do soin the illustration of my invention, and well-known forms of apparatuscan be used for them.

For the calling system an independentcall- 'ing-circuit common to manystations-such as theLaw or the American district systemmay be used.

I claim as my invention and desireto secure by Letters Patent I 1. In atelephone-exchange system,,a metallic-circuit telephone-line and a testreceiv- ;ing instrument at the central office, said line' ,beingnormally connectedv at the central of- ;fice butnot elsewhere on one ofits sides to one side of said test receiving instrumentand 1 open. onits other side to said instrument, and 1 said instrument being open tothe ground in lcombinati'on with an electric battery at the subscribersstation in the circuit of said line ;when it is not switched forconversation, a jswitching device to disconnect saidline from its normalconnectionrwith said test receiving finstrument when the line isswitched for conjversation, and a switch testing plug or deviceiadapted", at the will of the operator, to 0011- jinect said. instrumenton its other side to the ide of said line normally open to it,substanjtially as set forth. I

2. In a telephone-exchange system, two'or j'more multiple switchboardsat the central office, metallic-circuit lines connected to them ,andtest receiving instruments, one ateach fboard, each line being normallyconnected at .jthe central office but not elsewhere on one of ga sidesto each of saidtest'receiving instruiments, and said instruments being,open to fthe ground in. combination with electric batf teries, one inthe circuit of each line at its subscribers station When-the line isnotswitched ,for conversation, switching devices, one, at each board foreach line to disconnect the ;line from its normal connection with saidtest :rcceiving instruments, and switch testing plugs or devices, onefor each test receiving instrument, adapt'ed', at' the will of the operator, to connect its instrument on the other side to the normally openend of any of said lines, substantially as set forth.

3. In a telephone-exchange system, metallic-circuit lines and electricbatteries, one in the circuit of each line at the subscribers stationwhen the line is not switched for conversation, in combination withmultiple switchboards for said lines at the central ofiice, testreceiving instruments, one for each board, switches for said lines, onefor each line on each board, each switch having a pair of contact-pointsnormally in contact but opened to each other when its line is switchedfor conversation, one side of each line passing successively throughsaid pairs of contact-points of its switches on the different boards andthence connected to one side of each of said test receiving instrumentsand not connected to it elsewhere, and said instruments being open tothe ground, test bolts or pieces one for each line on each board and toeach of which the other side of its line is connected, and switchtestingplugs or devices, one for each of said instruments and each adapted, atthe will of the operator, to connect its instrument on the other side toany test bolt or piece located at its board, substantially as set forth.

4. In 'a telephone-exchange system, metallic-circuit lines, multipleswitchboards for said lines and switches, one on each board for eachline, in combination with test receiving instruments, one at each board,each instrument being open to the ground, and normally connected on oneside to one side or branch of each of said lines, but disconnected fromthe line when the line is switched for conversation, and connected onits other side to a switch testing plug or device, adapted, at the willof the operator, to be brought into connection with the other side orbranch of the line when the line is not in use, substantially as setforth.

In witness whereof I hereunto subscribe my name this 9th day of July, A.D. 1888.

MILO G. KELLOGG.

Witnesses:

MILTON HEAD, CALVIN DE WOLF.

